Excluding Sinn Fein from the Northern Ireland Executive would be a grave error, the prime minister has been warned.

Speaking on BBC Radio Ulster Sinn Fein's Martin McGuinness said any moves to remove his party from the power-sharing government in an effort to appease unionists would be a big mistake.

Tony Blair pledged to rebuild confidence in the Northern Ireland process after talks with the pro-Agreement parties and Irish premier Bertie Ahern at Hillsborough Castle, County Down, earlier this month.

Ulster Unionists are demanding that Sinn Fein be held to account for any breaches of the IRA ceasefire.

Martin McGuinness: Warned Tony Blair against making a big mistake

"There is a determined attempt being made by the Ulster Unionist Party, who appear to be setting a context for the battle within unionism for the next assembly elections, to effectively have Sinn Fein excluded from the executive," he said.

"We could be on the threshold of seeing Tony Blair make what possibly could be the biggest mistake that he has made in the course of this peace process."

Meanwhile, a senior ulster unionist has questioned the commitment of republicans to the peace process.

'Confidence'

The Culture Minister, Michael McGimpsey, has called on them to end their protests against Orange Order marches.

"It does seem that these protests are essentially naked sectarianism in action," he said.

Nationalist protesters engaged in serious rioting in west Belfast on Friday following a contentious parade in the area.

Twenty officers were injured in the violence when up to 100 petrol bombs were thrown and police fired more than 20 baton rounds.

On Wednesday, Ulster Unionist leader David Trimble urged the government to "get a grip on the situation and recreate some confidence in the community".

Mr Trimble said Mr Blair must come up with a procedure that engendered credibility and popular confidence.

It is not clear exactly what Mr Blair intends to do, to show that the government is taking a tougher line on paramilitaries.

However, he said he would put forward proposals to the parties before parliament goes into recess on 24 July.